When added they should be idealy +/- 5%, +/- 10% is acceptable.

Anything more than that you may want to look at adjusting your ve tables in your cruise areas.

 

i have a well know tuner working on my car and he is saying its my front O2 sensor, but at idle it read 14.7-15.3 on my aem UEGO and same at cruise though. even though im at stoich for asfrs could i still be geeting bad gasmileage due to front o2 going out?

 

Yes. Mine went out over the summer after one of my injectors took a dump. My gas mileage went from an avg of 25, to 22 on the next tank, to 19 after that with no change in driving habits during my daily commute. Put a new o2 in and back to normal. Your WB will keep reading what it is supposed to in this case, the ecu just keeps over compensating to keep it happy with the messed up readings it gets from the sensor crapping out.

There are a number of factors that affect your mileage, one of them being how much the ecu has to make corrections to the fueling based on the sensor feedback.

Glad your getting taken care of.

 

ok cool, i cant find any leaks.

i was just confused cause the AFRs are reading correctly. but im still getting bad fuel mileage.

but your saying thats normal to read correctly and still get crap mileage. its just getting lazy or on its way to being completly dead?

the current tune is to run in closed loop at idle and up to 2000 rpm at 2000 rpm the front o2 sensor takes over for cruise.

 

Yes, because the ecu is compensating to make sure it is near stoich at idle and cruising. The voltage in the sensor has bigger swings as the o2 sensor goes out, thus the ecu compensates more for the swings by add/subtracting fuel more often and in larger percentages.

 

Could be the fuel also. Winter blend has killed my mpg along with everyone else around my area that I've talked to. I'm not getting 150 to a tank though. Usually average +/- 200 in city.

 

yea i read that, and im all city driving as well. if i could get 200 to a tank id be happy!!!

 

have you checked the compression on all cylinders?

 

compression is 155 all across

 

Not necessarily our oxygen sensors are "heated". Basically it sends a specific voltage through the o2 sensor to warm it up so it can get the car running in closed loop as quickly as possible. A lot of time when there's an o2 sensor code it's because it didn't heat up quick enough.

The powertrain control module (PCM) provides a baseline voltage of about 450 mV on the oxygen sensor signal circuit. When the car is cold, the PCM detects the the internal resistance of the sensor is high. As the sensor warms up the resistance lowers and it starts producing voltage based on the amount of oxygen in the exhaust. When the PCM deceides that the time it took for the sensor to warm up is greater than the set specific time or that the voltage is inactive you'll get a p0134 code.

 

Read description

That's 4th gear 3000ish rpm if does that BS swinging it throws the code then after the code is thrown the AFRs are fine.

Think it's the o2?

 

I think this is what us happening, cause I'm in Utah and its cold as $#|t here. Does this mean that the sensors is going bad?

 

Anybody?

 

Unfortunately yeah. You check it with a dvom

 

Your poor fuel economy is most likely a combination of many factors.

The first factor is most likely due to colder temperature this time of year. Now that its getting colder out the car will definitely loose efficiency and use more fuel due to the difference in winter fuel. The engine also uses more of its fuel maintaining operating temps when its cold out. Have you change fuel brands recently, maybe one with more ethanol?

Secondly, maintenance plays a huge role in fuel efficiency. Lots of little issues can contribute to the overall performance of the engine. How is the air filter? if its dirty the engine will have to work harder to overcome the restriction loosing efficiency and fuel economy. Maybe the injectors have become dirty and the spray pattern is not as optimal as it should be causing the engine to not run as efficiently as it once did. Are you still running the test pipe? You haven't installed a CAT by chance have you?

Another huge factor is driving habits/routines have you change how you drive recently? New/different daily commute? maybe closer of farther away? On average are you driving faster then you did before? I know my evo gets much better fuel economy when I drive slow, such as cruising at 60 or less vers 75+.

Unfortunately, there probably isn't just one good answer to your problem, if there is and you do find out what it is please do share with the us.